Link to default branch when no rev is given
Created by: vanesa
Link to default branch when no rev is given. Fixes #407 .
Originally, if no rev was given, the Go-To-Github Url would link to "HEAD", which in Github would be the latest commit SHA instead of the master/default branch. This meant an additional step of switching to the default branch if one wanted to edit the file.
Instead of linking to "HEAD", this PR makes it that we link to the default branch.
This PR updates the CHANGELOG.md file to describe any user-facing changes.